Re: [PATCH] iio: humidity: hts221: fix division by zero in calibration data parsing

[Jonathan Cameron]

On Wed, 26 Aug 2026 17:09:49 +0300
Andy Shevchenko <andriy.shevchenko@xxxxxxxxx> wrote:

> On Tue, Aug 25, 2026 at 05:21:10PM +0800, Yang Zi wrote:
> > hts221_parse_temp_caldata() and hts221_parse_rh_caldata() compute the
> > sensor slope as ((cal_y1 - cal_y0) * 8000) / (cal_x1 - cal_x0). If the
> > device reports cal_x1 == cal_x0 the division causes a divide-by-zero
> > error.
> > 
> > Return -EINVAL when cal_x1 == cal_x0 in both functions before performing
> > the division.  
> 
> Do you have HW to test? Any fault injection perhaps?
> The problem with div-by-0 is that it's implementation defined, meaning
> that it's how compiler decides. Now, the question is, what will compiler
> do in the current code (no patch applied)?
> 
Whilst all this is true, the code shouldn't be relying on any particular
behavior.  So do we need to know?

Reality is the hardware is almost certainly never returning values where this
is true.

Jonathan

> ...
> 
> >          return err;  
> 
> >      cal_x1 = le16_to_cpu(val);  
> 
> >    
> 
> I would remove this blank line as it's coupled with the above.
> 
> > +    if (cal_x1 == cal_x0)
> > +        return -EINVAL;
> > +  
> 
> >      slope = &hw->sensors[HTS221_SENSOR_T].slope;
> >      b_gen = &hw->sensors[HTS221_SENSOR_T].b_gen;  
> 
> Ditto for the rest.
> 
>